Breath testers of the type which utilize an electronic detector are still relatively new and have significant advantages over the earlier chemical type detectors. Among these advantages are simplicity of use, light weight, and ease of portability and storage. Such units, for example of the type described in U.S. Pat. No. 3,877,291 have been employed in law enforcement work as "screening units," to provide an preliminary indication of a blood alcohol content. Related units have also been used to provide evidence for subsequent use in law enforcement proceedings. More recently related units have been constructed for operation by a coin-operated energizing arrangement for use, by way of example, in drinking establishments. Related background descriptions of such units are also set out in U.S. Pat. Nos. 3,764,270; 3,842,345; 3,886,786; 3,823,601; and 3,854,320, all of which are assigned to the assignee of this invention.
One drawback of such breath testers which employ an electronic detector is that the information signal can be misleading if the breath input signal comprises any anomalous chemical substance, such as acetone or ketone. Such material may be entrained in the exhaled breath of a person having diabetes, or a person adhering to one of the "fad" diets which radically change the blood chemistry, or a person who has imbibed an unusual liquid, one other than a normal alcoholic beverage. In general such an anomalous chemical substance is processed by the electronic detector to provide an information signal which can not be distinguished from an information signal having an amplitude signal denoting a high blood alcohol content.
It is therefore a primary consideration of this invention to provide a breath tester of the type having an electronic detector for developing an information signal connoting blood alcohol level, but which system is not susceptible to the production of an erroneous output by the introduction of an anomalous chemical substance as described above.